root/trunk/lisp/eshell/esh-cmd.el

;;; esh-cmd.el --- command invocation

;; Copyright (C) 1999, 2000, 2001, 2002, 2003, 2004,
;;   2005, 2006, 2007, 2008 Free Software Foundation, Inc.

;; Author: John Wiegley <johnw@gnu.org>

;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 3, or (at your option)
;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

(provide 'esh-cmd)

(eval-when-compile (require 'esh-maint))

(defgroup eshell-cmd nil
  "Executing an Eshell command is as simple as typing it in and
pressing <RET>.  There are several different kinds of commands,
however."
  :tag "Command invocation"
  ;; :link '(info-link "(eshell)Command invocation")
  :group 'eshell)

;;; Commentary:

;;;_* Invoking external commands
;;
;; External commands cause processes to be created, by loading
;; external executables into memory.  This is what most normal shells
;; do, most of the time.  For more information, see [External commands].
;;
;;;_* Invoking Lisp functions
;;
;; A Lisp function can be invoked using Lisp syntax, or command shell
;; syntax.  For example, to run `dired' to edit the current directory:
;;
;;   /tmp $ (dired ".")
;;
;; Or:
;;
;;   /tmp $ dired .
;;
;; The latter form is preferable, but the former is more precise,
;; since it involves no translations.  See [Argument parsing], to
;; learn more about how arguments are transformed before passing them
;; to commands.
;;
;; Ordinarily, if 'dired' were also available as an external command,
;; the external version would be called in preference to any Lisp
;; function of the same name.  To change this behavior so that Lisp
;; functions always take precedence, set
;; `eshell-prefer-lisp-functions' to t.

(defcustom eshell-prefer-lisp-functions nil
  "*If non-nil, prefer Lisp functions to external commands."
  :type 'boolean
  :group 'eshell-cmd)

;;;_* Alias functions
;;
;; Whenever a command is specified using a simple name, such as 'ls',
;; Eshell will first look for a Lisp function of the name `eshell/ls'.
;; If it exists, it will be called in preference to any other command
;; which might have matched the name 'ls' (such as command aliases,
;; external commands, Lisp functions of that name, etc).
;;
;; This is the most flexible mechanism for creating new commands,
;; since it does not pollute the global namespace, yet allows you to
;; use all of Lisp's facilities to define that piece of functionality.
;; Most of Eshell's "builtin" commands are defined as alias functions.
;;
;;;_* Lisp arguments
;;
;; It is possible to invoke a Lisp form as an argument.  This can be
;; done either by specifying the form as you might in Lisp, or by
;; using the '$' character to introduce a value-interpolation:
;;
;;   echo (+ 1 2)
;;
;; Or
;;
;;   echo $(+ 1 2)
;;
;; The two forms are equivalent.  The second is required only if the
;; form being interpolated is within a string, or is a subexpression
;; of a larger argument:
;;
;;   echo x$(+ 1 2) "String $(+ 1 2)"
;;
;; To pass a Lisp symbol as a argument, use the alternate quoting
;; syntax, since the single quote character is far too overused in
;; shell syntax:
;;
;;   echo #'lisp-symbol
;;
;; Backquote can also be used:
;;
;;   echo `(list ,lisp-symbol)
;;
;; Lisp arguments are identified using the following regexp:

(defcustom eshell-lisp-regexp "\\([(`]\\|#'\\)"
  "*A regexp which, if matched at beginning of an argument, means Lisp.
Such arguments will be passed to `read', and then evaluated."
  :type 'regexp
  :group 'eshell-cmd)

;;;_* Command hooks
;;
;; There are several hooks involved with command execution, which can
;; be used either to change or augment Eshell's behavior.

(defcustom eshell-pre-command-hook nil
  "*A hook run before each interactive command is invoked."
  :type 'hook
  :group 'eshell-cmd)

(defcustom eshell-post-command-hook nil
  "*A hook run after each interactive command is invoked."
  :type 'hook
  :group 'eshell-cmd)

(defcustom eshell-prepare-command-hook nil
  "*A set of functions called to prepare a named command.
The command name and its argument are in `eshell-last-command-name'
and `eshell-last-arguments'.  The functions on this hook can change
the value of these symbols if necessary.

To prevent a command from executing at all, set
`eshell-last-command-name' to nil."
  :type 'hook
  :group 'eshell-cmd)

(defcustom eshell-named-command-hook nil
  "*A set of functions called before a named command is invoked.
Each function will be passed the command name and arguments that were
passed to `eshell-named-command'.

If any of the functions returns a non-nil value, the named command
will not be invoked, and that value will be returned from
`eshell-named-command'.

In order to substitute an alternate command form for execution, the
hook function should throw it using the tag `eshell-replace-command'.
For example:

  (add-hook 'eshell-named-command-hook 'subst-with-cd)
  (defun subst-with-cd (command args)
    (throw 'eshell-replace-command
           (eshell-parse-command \"cd\" args)))

Although useless, the above code will cause any non-glob, non-Lisp
command (i.e., 'ls' as opposed to '*ls' or '(ls)') to be replaced by a
call to `cd' using the arguments that were passed to the function."
  :type 'hook
  :group 'eshell-cmd)

(defcustom eshell-pre-rewrite-command-hook
  '(eshell-no-command-conversion
    eshell-subcommand-arg-values)
  "*A hook run before command rewriting begins.
The terms of the command to be rewritten is passed as arguments, and
may be modified in place.  Any return value is ignored."
  :type 'hook
  :group 'eshell-cmd)

(defcustom eshell-rewrite-command-hook
  '(eshell-rewrite-for-command
    eshell-rewrite-while-command
    eshell-rewrite-if-command
    eshell-rewrite-sexp-command
    eshell-rewrite-initial-subcommand
    eshell-rewrite-named-command)
  "*A set of functions used to rewrite the command argument.
Once parsing of a command line is completed, the next step is to
rewrite the initial argument into something runnable.

A module may wish to associate special behavior with certain argument
syntaxes at the beginning of a command line.  They are welcome to do
so by adding a function to this hook.  The first function to return a
substitute command form is the one used.  Each function is passed the
command's full argument list, which is a list of sexps (typically
forms or strings)."
  :type 'hook
  :group 'eshell-cmd)

(defcustom eshell-post-rewrite-command-hook nil
  "*A hook run after command rewriting is finished.
Each function is passed the symbol containing the rewritten command,
which may be modified directly.  Any return value is ignored."
  :type 'hook
  :group 'eshell-cmd)

(defcustom eshell-complex-commands '("ls")
  "*A list of commands names or functions, that determine complexity.
That is, if a command is defined by a function named eshell/NAME,
and NAME is part of this list, it is invoked as a complex command.
Complex commands are always correct, but run much slower.  If a
command works fine without being part of this list, then it doesn't
need to be.

If an entry is a function, it will be called with the name, and should
return non-nil if the command is complex."
  :type '(repeat :tag "Commands"
                 (choice (string :tag "Name")
                         (function :tag "Predicate")))
  :group 'eshell-cmd)

;;; Code:

(require 'esh-util)
(unless (eshell-under-xemacs-p)
  (require 'eldoc))
(require 'esh-arg)
(require 'esh-proc)
(require 'esh-ext)

;;; User Variables:

(defcustom eshell-cmd-load-hook '(eshell-cmd-initialize)
  "*A hook that gets run when `eshell-cmd' is loaded."
  :type 'hook
  :group 'eshell-cmd)

(defcustom eshell-debug-command nil
  "*If non-nil, enable debugging code.  SSLLOOWW.
This option is only useful for reporting bugs.  If you enable it, you
will have to visit the file 'eshell-cmd.el' and run the command
\\[eval-buffer]."
  :type 'boolean
  :group 'eshell-cmd)

(defcustom eshell-deferrable-commands
  '(eshell-named-command
    eshell-lisp-command
    eshell-process-identity)
  "*A list of functions which might return an ansychronous process.
If they return a process object, execution of the calling Eshell
command will wait for completion (in the background) before finishing
the command."
  :type '(repeat function)
  :group 'eshell-cmd)

(defcustom eshell-subcommand-bindings
  '((eshell-in-subcommand-p t)
    (default-directory default-directory)
    (process-environment (eshell-copy-environment)))
  "*A list of `let' bindings for subcommand environments."
  :type 'sexp
  :group 'eshell-cmd)

(put 'risky-local-variable 'eshell-subcommand-bindings t)

(defvar eshell-ensure-newline-p nil
  "If non-nil, ensure that a newline is emitted after a Lisp form.
This can be changed by Lisp forms that are evaluated from the Eshell
command line.")

;;; Internal Variables:

(defvar eshell-current-command nil)
(defvar eshell-command-name nil)
(defvar eshell-command-arguments nil)
(defvar eshell-in-pipeline-p nil)
(defvar eshell-in-subcommand-p nil)
(defvar eshell-last-arguments nil)
(defvar eshell-last-command-name nil)
(defvar eshell-last-async-proc nil
  "When this foreground process completes, resume command evaluation.")

;;; Functions:

(defsubst eshell-interactive-process ()
  "Return currently running command process, if non-Lisp."
  eshell-last-async-proc)

(defun eshell-cmd-initialize ()
  "Initialize the Eshell command processing module."
  (set (make-local-variable 'eshell-current-command) nil)
  (set (make-local-variable 'eshell-command-name) nil)
  (set (make-local-variable 'eshell-command-arguments) nil)
  (set (make-local-variable 'eshell-last-arguments) nil)
  (set (make-local-variable 'eshell-last-command-name) nil)
  (set (make-local-variable 'eshell-last-async-proc) nil)

  (add-hook 'eshell-kill-hook 'eshell-resume-command nil t)

  ;; make sure that if a command is over, and no process is being
  ;; waited for, that `eshell-current-command' is set to nil.  This
  ;; situation can occur, for example, if a Lisp function results in
  ;; `debug' being called, and the user then types \\[top-level]
  (add-hook 'eshell-post-command-hook
            (function
             (lambda ()
               (setq eshell-current-command nil
                     eshell-last-async-proc nil))) nil t)

  (add-hook 'eshell-parse-argument-hook
            'eshell-parse-subcommand-argument nil t)
  (add-hook 'eshell-parse-argument-hook
            'eshell-parse-lisp-argument nil t)

  (when (eshell-using-module 'eshell-cmpl)
    (add-hook 'pcomplete-try-first-hook
              'eshell-complete-lisp-symbols nil t)))

(eshell-deftest var last-result-var
  "\"last result\" variable"
  (eshell-command-result-p "+ 1 2; + $$ 2" "3\n5\n"))

(eshell-deftest var last-result-var2
  "\"last result\" variable"
  (eshell-command-result-p "+ 1 2; + $$ $$" "3\n6\n"))

(eshell-deftest var last-arg-var
  "\"last arg\" variable"
  (eshell-command-result-p "+ 1 2; + $_ 4" "3\n6\n"))

(defun eshell-complete-lisp-symbols ()
  "If there is a user reference, complete it."
  (let ((arg (pcomplete-actual-arg)))
    (when (string-match (concat "\\`" eshell-lisp-regexp) arg)
      (setq pcomplete-stub (substring arg (match-end 0))
            pcomplete-last-completion-raw t)
      (throw 'pcomplete-completions
             (all-completions pcomplete-stub obarray 'boundp)))))

;; Command parsing

(defun eshell-parse-command (command &optional args top-level)
  "Parse the COMMAND, adding ARGS if given.
COMMAND can either be a string, or a cons cell demarcating a buffer
region.  TOP-LEVEL, if non-nil, means that the outermost command (the
user's input command) is being parsed, and that pre and post command
hooks should be run before and after the command."
  (let* (sep-terms
         (terms
          (append
           (if (consp command)
               (eshell-parse-arguments (car command) (cdr command))
             (let ((here (point))
                   (inhibit-point-motion-hooks t)
                   after-change-functions)
               (insert command)
               (prog1
                   (eshell-parse-arguments here (point))
                 (delete-region here (point)))))
           args))
         (commands
          (mapcar
           (function
            (lambda (cmd)
              (if (or (not (car sep-terms))
                      (string= (car sep-terms) ";"))
                  (setq cmd
                        (eshell-parse-pipeline cmd (not (car sep-terms))))
                (setq cmd
                      (list 'eshell-do-subjob
                            (list 'list (eshell-parse-pipeline cmd)))))
              (setq sep-terms (cdr sep-terms))
              (if eshell-in-pipeline-p
                  cmd
                (list 'eshell-trap-errors cmd))))
           (eshell-separate-commands terms "[&;]" nil 'sep-terms))))
    (let ((cmd commands))
      (while cmd
        (if (cdr cmd)
            (setcar cmd (list 'eshell-commands (car cmd))))
        (setq cmd (cdr cmd))))
    (setq commands
          (append (list 'progn)
                  (if top-level
                      (list '(run-hooks 'eshell-pre-command-hook)))
                  (if (not top-level)
                      commands
                    (list
                     (list 'catch (quote 'top-level)
                           (append (list 'progn) commands))
                     '(run-hooks 'eshell-post-command-hook)))))
    (if top-level
        (list 'eshell-commands commands)
      commands)))

(defun eshell-debug-show-parsed-args (terms)
  "Display parsed arguments in the debug buffer."
  (ignore
   (if eshell-debug-command
       (eshell-debug-command "parsed arguments" terms))))

(defun eshell-no-command-conversion (terms)
  "Don't convert the command argument."
  (ignore
   (if (and (listp (car terms))
            (eq (caar terms) 'eshell-convert))
       (setcar terms (cadr (car terms))))))

(defun eshell-subcommand-arg-values (terms)
  "Convert subcommand arguments {x} to ${x}, in order to take their values."
  (setq terms (cdr terms))              ; skip command argument
  (while terms
    (if (and (listp (car terms))
             (eq (caar terms) 'eshell-as-subcommand))
        (setcar terms (list 'eshell-convert
                            (list 'eshell-command-to-value
                                  (car terms)))))
    (setq terms (cdr terms))))

(defun eshell-rewrite-sexp-command (terms)
  "Rewrite a sexp in initial position, such as '(+ 1 2)'."
  ;; this occurs when a Lisp expression is in first position
  (if (and (listp (car terms))
           (eq (caar terms) 'eshell-command-to-value))
      (car (cdar terms))))

(eshell-deftest cmd lisp-command
  "Evaluate Lisp command"
  (eshell-command-result-p "(+ 1 2)" "3"))

(eshell-deftest cmd lisp-command-args
  "Evaluate Lisp command (ignore args)"
  (eshell-command-result-p "(+ 1 2) 3" "3"))

(defun eshell-rewrite-initial-subcommand (terms)
  "Rewrite a subcommand in initial position, such as '{+ 1 2}'."
  (if (and (listp (car terms))
           (eq (caar terms) 'eshell-as-subcommand))
      (car terms)))

(eshell-deftest cmd subcommand
  "Run subcommand"
  (eshell-command-result-p "{+ 1 2}" "3\n"))

(eshell-deftest cmd subcommand-args
  "Run subcommand (ignore args)"
  (eshell-command-result-p "{+ 1 2} 3" "3\n"))

(eshell-deftest cmd subcommand-lisp
  "Run subcommand + Lisp form"
  (eshell-command-result-p "{(+ 1 2)}" "3\n"))

(defun eshell-rewrite-named-command (terms)
  "If no other rewriting rule transforms TERMS, assume a named command."
  (let ((sym (if eshell-in-pipeline-p
                 'eshell-named-command*
               'eshell-named-command))
        (cmd (car terms))
        (args (cdr terms)))
    (if args
        (list sym cmd (append (list 'list) (cdr terms)))
      (list sym cmd))))

(eshell-deftest cmd named-command
  "Execute named command"
  (eshell-command-result-p "+ 1 2" "3\n"))

(eval-when-compile
  (defvar eshell-command-body)
  (defvar eshell-test-body))

(defsubst eshell-invokify-arg (arg &optional share-output silent)
  "Change ARG so it can be invoked from a structured command.

SHARE-OUTPUT, if non-nil, means this invocation should share the
current output stream, which is separately redirectable.  SILENT
means the user and/or any redirections shouldn't see any output
from this command.  If both SHARE-OUTPUT and SILENT are non-nil,
the second is ignored."
  ;; something that begins with `eshell-convert' means that it
  ;; intends to return a Lisp value.  We want to get past this,
  ;; but if it's not _actually_ a value interpolation -- in which
  ;; we leave it alone.  In fact, the only time we muck with it
  ;; is in the case of a {subcommand} that has been turned into
  ;; the interpolation, ${subcommand}, by the parser because it
  ;; didn't know better.
  (if (and (listp arg)
           (eq (car arg) 'eshell-convert)
           (eq (car (cadr arg)) 'eshell-command-to-value))
      (if share-output
          (cadr (cadr arg))
        (list 'eshell-commands (cadr (cadr arg))
              silent))
    arg))

(defun eshell-rewrite-for-command (terms)
  "Rewrite a `for' command into its equivalent Eshell command form.
Because the implementation of `for' relies upon conditional evaluation
of its argument (i.e., use of a Lisp special form), it must be
implemented via rewriting, rather than as a function."
  (if (and (stringp (car terms))
           (string= (car terms) "for")
           (stringp (nth 2 terms))
           (string= (nth 2 terms) "in"))
      (let ((body (car (last terms))))
        (setcdr (last terms 2) nil)
        (list
         'let (list (list 'for-items
                          (append
                           (list 'append)
                           (mapcar
                            (function
                             (lambda (elem)
                               (if (listp elem)
                                   elem
                                 (list 'list elem))))
                            (cdr (cddr terms)))))
                    (list 'eshell-command-body
                          (list 'quote (list nil)))
                    (list 'eshell-test-body
                          (list 'quote (list nil))))
         (list
          'progn
          (list
           'while (list 'car (list 'symbol-value
                                   (list 'quote 'for-items)))
           (list
            'progn
            (list 'let
                  (list (list (intern (cadr terms))
                              (list 'car
                                    (list 'symbol-value
                                          (list 'quote 'for-items)))))
                  (list 'eshell-protect
                        (eshell-invokify-arg body t)))
            (list 'setcar 'for-items
                  (list 'cadr
                        (list 'symbol-value
                              (list 'quote 'for-items))))
            (list 'setcdr 'for-items
                  (list 'cddr
                        (list 'symbol-value
                              (list 'quote 'for-items))))))
          (list 'eshell-close-handles
                'eshell-last-command-status
                (list 'list (quote 'quote)
                      'eshell-last-command-result)))))))

(defun eshell-structure-basic-command (func names keyword test body
                                            &optional else vocal-test)
  "With TERMS, KEYWORD, and two NAMES, structure a basic command.
The first of NAMES should be the positive form, and the second the
negative.  It's not likely that users should ever need to call this
function.

If VOCAL-TEST is non-nil, it means output from the test should be
shown, as well as output from the body."
  ;; If the test form begins with `eshell-convert', it means
  ;; something data-wise will be returned, and we should let
  ;; that determine the truth of the statement.
  (unless (eq (car test) 'eshell-convert)
    (setq test
          (list 'progn test
                (list 'eshell-exit-success-p))))

  ;; should we reverse the sense of the test?  This depends
  ;; on the `names' parameter.  If it's the symbol nil, yes.
  ;; Otherwise, it can be a pair of strings; if the keyword
  ;; we're using matches the second member of that pair (a
  ;; list), we should reverse it.
  (if (or (eq names nil)
          (and (listp names)
               (string= keyword (cadr names))))
      (setq test (list 'not test)))

  ;; finally, create the form that represents this structured
  ;; command
  (list
   'let (list (list 'eshell-command-body
                    (list 'quote (list nil)))
              (list 'eshell-test-body
                    (list 'quote (list nil))))
   (list func test body else)
   (list 'eshell-close-handles
         'eshell-last-command-status
         (list 'list (quote 'quote)
               'eshell-last-command-result))))

(defun eshell-rewrite-while-command (terms)
  "Rewrite a `while' command into its equivalent Eshell command form.
Because the implementation of `while' relies upon conditional
evaluation of its argument (i.e., use of a Lisp special form), it
must be implemented via rewriting, rather than as a function."
  (if (and (stringp (car terms))
           (member (car terms) '("while" "until")))
      (eshell-structure-basic-command
       'while '("while" "until") (car terms)
       (eshell-invokify-arg (cadr terms) nil t)
       (list 'eshell-protect
             (eshell-invokify-arg (car (last terms)) t)))))

(defun eshell-rewrite-if-command (terms)
  "Rewrite an `if' command into its equivalent Eshell command form.
Because the implementation of `if' relies upon conditional
evaluation of its argument (i.e., use of a Lisp special form), it
must be implemented via rewriting, rather than as a function."
  (if (and (stringp (car terms))
           (member (car terms) '("if" "unless")))
      (eshell-structure-basic-command
       'if '("if" "unless") (car terms)
       (eshell-invokify-arg (cadr terms) nil t)
       (list 'eshell-protect
             (eshell-invokify-arg
              (if (= (length terms) 4)
                  (car (last terms 2))
                (car (last terms))) t))
       (if (= (length terms) 4)
           (list 'eshell-protect
                 (eshell-invokify-arg
                  (car (last terms)))) t))))

(defun eshell-exit-success-p ()
  "Return non-nil if the last command was \"successful\".
For a bit of Lisp code, this means a return value of non-nil.
For an external command, it means an exit code of 0."
  (if (save-match-data
        (string-match "#<\\(Lisp object\\|function .*\\)>"
                      eshell-last-command-name))
      eshell-last-command-result
    (= eshell-last-command-status 0)))

(defun eshell-parse-pipeline (terms &optional final-p)
  "Parse a pipeline from TERMS, return the appropriate Lisp forms."
  (let* (sep-terms
         (bigpieces (eshell-separate-commands terms "\\(&&\\|||\\)"
                                              nil 'sep-terms))
         (bp bigpieces)
         (results (list t))
         final)
    (while bp
      (let ((subterms (car bp)))
        (let* ((pieces (eshell-separate-commands subterms "|"))
               (p pieces))
          (while p
            (let ((cmd (car p)))
              (run-hook-with-args 'eshell-pre-rewrite-command-hook cmd)
              (setq cmd (run-hook-with-args-until-success
                         'eshell-rewrite-command-hook cmd))
              (run-hook-with-args 'eshell-post-rewrite-command-hook 'cmd)
              (setcar p cmd))
            (setq p (cdr p)))
          (nconc results
                 (list
                  (if (<= (length pieces) 1)
                      (car pieces)
                    (assert (not eshell-in-pipeline-p))
                    (list 'eshell-execute-pipeline
                          (list 'quote pieces))))))
        (setq bp (cdr bp))))
    ;; `results' might be empty; this happens in the case of
    ;; multi-line input
    (setq results (cdr results)
          results (nreverse results)
          final (car results)
          results (cdr results)
          sep-terms (nreverse sep-terms))
    (while results
      (assert (car sep-terms))
      (setq final (eshell-structure-basic-command
                   'if (string= (car sep-terms) "&&") "if"
                   (list 'eshell-protect (car results))
                   (list 'eshell-protect final)
                   nil t)
            results (cdr results)
            sep-terms (cdr sep-terms)))
    final))

(defun eshell-parse-subcommand-argument ()
  "Parse a subcommand argument of the form '{command}'."
  (if (and (not eshell-current-argument)
           (not eshell-current-quoted)
           (eq (char-after) ?\{)
           (or (= (point-max) (1+ (point)))
               (not (eq (char-after (1+ (point))) ?\}))))
      (let ((end (eshell-find-delimiter ?\{ ?\})))
        (if (not end)
            (throw 'eshell-incomplete ?\{)
          (when (eshell-arg-delimiter (1+ end))
            (prog1
                (list 'eshell-as-subcommand
                      (eshell-parse-command (cons (1+ (point)) end)))
              (goto-char (1+ end))))))))

(defun eshell-parse-lisp-argument ()
  "Parse a Lisp expression which is specified as an argument."
  (if (and (not eshell-current-argument)
           (not eshell-current-quoted)
           (looking-at eshell-lisp-regexp))
      (let* ((here (point))
             (obj
              (condition-case err
                  (read (current-buffer))
                (end-of-file
                 (throw 'eshell-incomplete ?\()))))
        (if (eshell-arg-delimiter)
            (list 'eshell-command-to-value
                  (list 'eshell-lisp-command (list 'quote obj)))
          (ignore (goto-char here))))))

(defun eshell-separate-commands (terms separator &optional
                                       reversed last-terms-sym)
  "Separate TERMS using SEPARATOR.
If REVERSED is non-nil, the list of separated term groups will be
returned in reverse order.  If LAST-TERMS-SYM is a symbol, its value
will be set to a list of all the separator operators found (or '(list
nil)' if none)."
  (let ((sub-terms (list t))
        (eshell-sep-terms (list t))
        subchains)
    (while terms
      (if (and (consp (car terms))
               (eq (caar terms) 'eshell-operator)
               (string-match (concat "^" separator "$")
                             (nth 1 (car terms))))
          (progn
            (nconc eshell-sep-terms (list (nth 1 (car terms))))
            (setq subchains (cons (cdr sub-terms) subchains)
                  sub-terms (list t)))
        (nconc sub-terms (list (car terms))))
      (setq terms (cdr terms)))
    (if (> (length sub-terms) 1)
        (setq subchains (cons (cdr sub-terms) subchains)))
    (if reversed
        (progn
          (if last-terms-sym
              (set last-terms-sym (reverse (cdr eshell-sep-terms))))
          subchains)                    ; already reversed
      (if last-terms-sym
          (set last-terms-sym (cdr eshell-sep-terms)))
      (nreverse subchains))))

;;_* Command evaluation macros
;;
;; The structure of the following macros is very important to
;; `eshell-do-eval' [Iterative evaluation]:
;;
;; @ Don't use forms that conditionally evaluate their arguments, such
;;   as `setq', `if', `while', `let*', etc.  The only special forms
;;   that can be used are `let', `condition-case' and
;;   `unwind-protect'.
;;
;; @ The main body of a `let' can contain only one form.  Use `progn'
;;   if necessary.
;;
;; @ The two `special' variables are `eshell-current-handles' and
;;   `eshell-current-subjob-p'.  Bind them locally with a `let' if you
;;   need to change them.  Change them directly only if your intention
;;   is to change the calling environment.

(defmacro eshell-do-subjob (object)
  "Evaluate a command OBJECT as a subjob.
We indicate that the process was run in the background by returning it
ensconced in a list."
  `(let ((eshell-current-subjob-p t))
     ,object))

(defmacro eshell-commands (object &optional silent)
  "Place a valid set of handles, and context, around command OBJECT."
  `(let ((eshell-current-handles
          (eshell-create-handles ,(not silent) 'append))
         eshell-current-subjob-p)
     ,object))

(defmacro eshell-trap-errors (object)
  "Trap any errors that occur, so they are not entirely fatal.
Also, the variable `eshell-this-command-hook' is available for the
duration of OBJECT's evaluation.  Note that functions should be added
to this hook using `nconc', and *not* `add-hook'.

Someday, when Scheme will become the dominant Emacs language, all of
this grossness will be made to disappear by using `call/cc'..."
  `(let ((eshell-this-command-hook (list 'ignore)))
     (eshell-condition-case err
         (prog1
             ,object
           (run-hooks 'eshell-this-command-hook))
       (error
        (run-hooks 'eshell-this-command-hook)
        (eshell-errorn (error-message-string err))
        (eshell-close-handles 1)))))

(defmacro eshell-copy-handles (object)
  "Duplicate current I/O handles, so OBJECT works with its own copy."
  `(let ((eshell-current-handles
          (eshell-create-handles
           (car (aref eshell-current-handles
                      eshell-output-handle)) nil
           (car (aref eshell-current-handles
                      eshell-error-handle)) nil)))
     ,object))

(defmacro eshell-protect (object)
  "Protect I/O handles, so they aren't get closed after eval'ing OBJECT."
  `(progn
     (eshell-protect-handles eshell-current-handles)
     ,object))

(defmacro eshell-do-pipelines (pipeline)
  "Execute the commands in PIPELINE, connecting each to one another."
  (when (setq pipeline (cadr pipeline))
    `(eshell-copy-handles
      (progn
        ,(when (cdr pipeline)
           `(let (nextproc)
              (progn
                (set 'nextproc
                     (eshell-do-pipelines (quote ,(cdr pipeline))))
                (eshell-set-output-handle ,eshell-output-handle
                                          'append nextproc)
                (eshell-set-output-handle ,eshell-error-handle
                                          'append nextproc)
                (set 'tailproc (or tailproc nextproc)))))
        ,(let ((head (car pipeline)))
           (if (memq (car head) '(let progn))
               (setq head (car (last head))))
           (when (memq (car head) eshell-deferrable-commands)
             (ignore
              (setcar head
                      (intern-soft
                       (concat (symbol-name (car head)) "*"))))))
        ,(car pipeline)))))

(defmacro eshell-do-pipelines-synchronously (pipeline)
  "Execute the commands in PIPELINE in sequence synchronously.
Output of each command is passed as input to the next one in the pipeline.
This is used on systems where `start-process' is not supported."
  (when (setq pipeline (cadr pipeline))
    `(let (result)
       (progn
         ,(when (cdr pipeline)
            `(let (output-marker)
               (progn
                 (set 'output-marker ,(point-marker))
                 (eshell-set-output-handle ,eshell-output-handle
                                           'append output-marker)
                 (eshell-set-output-handle ,eshell-error-handle
                                           'append output-marker))))